Amplifier connection system



Patented eb. 19, 1935 PATENT OFFICE,

1,992,063 AMPLIFIER CONNECTION SYSTEM Albrecht Forstmann, Berlin, Germany No Drawing.

Application December. 29, 1928,

Serial No. 329,315. In Germany December 30, 1927 8 Claims.

This invention relates to a connection system for amplifiers.

The correction of amplifications, or distortions which are caused by the cable attenuation in the transmission of frequency ranges as a result of transmission not proportional to the amplitude, is well known. For this purpose connection means are employed which, generally speaking, perform compensation by reason of the fact that the more greatly amplified or less attenuated frequencies are reduced in their amplitude. The said connection means, for example networks, filters, tuned circuits and the like, generally use active resonances.

The primary object of the arrangements according to the present invention is as follows: By the provision of tubes compensation is produced by the fact that the maximum impedance of the external loading, which in this case occurs at the highest audio frequency, is equal or approximately equal to the internal tube resistance. For all lower audio frequencies the external impedance in this case is smaller, and this means that the high audio frequencies, since the optimum of the output exists in the case thereof, are better reproduced than low audio frequencies. It is possible to also connect a plurality of tubes in cascade, and in this case it will be desirable in the voltage amplification stages to'make the maximum external load (for the highest audio frequency) approximately equal to four times the amount of the internal tube resistance.

From this example a rule of general validity can be derived for the following deductions: for all frequencies to be preferredin the aforesaid example the high audio frequencies were preferred--in case of the output amplification, the effective external impedance must be equal to the internal resistance in order to establish the condition for the optimum of theo'utput, in case of the potential'amplification however, the maximum value of the effective external impedance must approximately be equal to four times the said internal resistance. This is synonymous with the declaration, that for all frequencies not to be preferentially amplified or transmitted the conditions just stated must be avoided: in this case therefore in the output amplification the condition due to the optimum of the output must be avoided that is to say, the effective external impedance must be as unlike as possible to the internal tube resistance: in the potential amplification stages the efiective external. impedance in this case must be small compared with four times the said internal tube resistanceand this tube resistance.

According to this invention there is provided a thermionic amplifier system for information transmission over cables or by wireless and with means for compensating distortions caused before and/or after the amplification of the signals'in said system by transmission, or amplification in other stages of the transmission not proportional in amplitude, characterized by the cOrrectionbeing produced by the provision of an effective external impedance in the plate circuit of the tube or tubes in the potential amplification stages in which the compensation is to take place and for frequencies mostly to be preferred which is approximately equal to four times the internal tube resistance.

Further according to this invention there is provided an amplifier system constructed in accordance with the preceding paragraph characterized by the fact that for all frequencies not preferentially to be transmitted or to be amplifled, the efiective external impedance, in the output amplification stage, is either relatively much 25 greater or relatively much smaller than the internal resistance, and in the potential amplification stages, is always relatively much smaller than the said internal tube resistance.

Again according to this invention there is provided an amplifier system constructed in accordance with the two preceding paragraphs applicable to radio frequencies as well as to audio frequencies, characterized by the fact that in one or more amplification stages, a preferential amplification of the low audio frequencies (the low modulation frequencies), and in one or more amplification stages, a preferential amplification of the high audio frequencies (the high modulation frequencies), is produced in such a manner that in the whole amplifier an amplification of all frequencies proportional to amplitudes is effected,

whereby for all frequencies preferentially to be amplifiedthe effective external impedance in the I plate circuit of the tube or tubes in the potential amplification stages, equals approximately four times the internal resistance of the said tubes as already'mentioned, and in the .output amplification stage, the effective external impedance in the plate circuit of the tube equals approximately the internal resistance of said tube.

Further according to this invention there is provided an amplifier system constructed in accordance with the three preceding paragraphs characterized by using in one, several or .all

stages, tubes having a relatively small reciprocal of amplification factor.

Furthermore, according to this invention there is provided an amplifier system constructed in accordance with the four preceding paragraphs characterized by multiple grid tubes being used in one, several or all of the amplifier stages.

In the transmission of intelligence by cables it is possible to employ such cable-attenuation compensating arrangements either in front of or behind the cable, or both.

In the wireless transmission of intelligence it is possible on the one hand to produce on the transmitting side a preferred amplification of the high audio frequencies by employing the arrangement on which the present invention is based, while on the other hand it is also possible to compensate with the arrangements in question detrimental effect on the side bands caused by large radio frequency amplification.

An additional advantage resides in the fact that by the use of tubes having large internal resistance and small reciprocal of the amplification factor in the radio frequency amplification stage or stages, a distortion of the side bands may be intentionally produced. It is thus possible on the one hand to obtain quite an exceptional amplification value per stage, and at the same time to considerably, increase per stage the selectivity, which obviously involves side band distortion. The linear distortions thus caused are then compensated by the audio frequency stage or stages in the manner indicated.

Despite unfavorable output adaptation large outputs will be obtained if the reciprocal of the amplification'factor of the output is made very small, since in this case despite the merely slight deviation between static characteristic of the tubes and the dynamic working characteristic existing in the case of low audio frequencies a correspondingly large potential amplification is present for obtaining a corresponding output.

By application on the one hand of the anode screening grid connection and furthermore by employing the space charge grid connection (the whole ascent of the characteristic charge curve occurs in a grid potential range which is approximately 1-2 volts greater than the drop of potential at the filament) it is possible to dispose the straight part of the tube characteristics within the range of the negative grid potential. It is naturally also possible to work within range of the positive grid potential, and in this case the tube preceding in cascade does not function as a stage of a voltage amplifier but has to furnish energy and therefore the electric data of the plate circuit must be chosen in accordance with those of the plate circuit of an output stage.

It is furthermore possible, and this is of particular advantage in the case of very small resulting reciprocals of the amplification factor (a reciprocal of .1% may be mentioned by way of example) to employ both the screening grid connection as well as the space charge grid connection. In this case, the internal resistance, being equal to the quotient of the amplification factor and the steepness, is correspondingly high. For reasons known per se the use of the space charge connection permits modulation of the whole straight characteristic portion with a grid change potential which conforms with approximately half of the drop of potential at the filament. The use of the screening grid connection allows, generally speaking, the use of lower anode potentials.

In the same manner as side band distortions in high frequency amplifiers may be intentionally produced artifically with increase of the amplification value, it is furthermore possible while increasing the amplifying value to produce a linear distortion of high modulation frequencies in an audio frequency amplifier, in which case tubes may also be employed having a very small reciprocal of the amplification.

In order to simplify the construction of the apparatus and also control thereof, it will in many cases be preferable in placeof a plurality of tubes to employ multiple or multi-system tubes, whereby the whole connection system may furthermore be disposed wholly or in part within the tubes.

The general idea upon which the invention is based accordingly resides in producing both 001'- rections as well as intentional distortions by means of the thermionic tubes of the various stages of an amplifying arrangement.

WhatI claim as new and desire to secure by Letters Patent is:

1. The method of thermionic amplification in transmission systems, comprising amplifying, in a potential amplifier, all frequencies of the frequency band to be transmitted, selecting one of the two limit frequencies of said band for more intense amplification in said amplifier than the non-selected frequencies, determining the impedance of a frequency-dependent resistor in the plate circuit of said amplifier so that, for the selected limit frequency, the impedance is of the order of, but not more than, four times the internal resistance of the tube in said amplifier, and, for the non-selected frequencies, the impedance is less than the said internal resistance.

2. The method of thermionic amplification in transmission systems, comprising amplifying, in a multistage potential amplifier, all frequencies of the frequency band to be transmitted, selecting certain limit frequencies, in certain stages of said amplifier, for more intense amplification than the non-selected frequencies, determining the impedances of frequency-dependent resistors in the plate circuits of the tubes of those stages of said amplifier in which a limit frequency has been selected, so that, for the selected limit frequencies, the impedances are of the order of, but not more than, four times the internal resistances of the tubes in the stages in which a limit frequency has been selected, and, for the non-selected frequencies, the impedances are less than the said internal resistances.

3. The method of thermionic potential and power amplification in transmission systems, comprising amplifying, in an amplifier having a potential and a power stage, all frequencies of the frequency band to be transmitted, selecting, in the potential stage of said amplifier, one of the two limit frequencies of said band for more intense amplification than the non-selected frequencies, determining the impedance of a frequency-dependent resistor in the plate circuit of the potential stage of said amplifier so that, for the selected limit frequency, the impedance is of the order of, but not more than, four times the internal resistance of the tube in the potential stage of said amplifier, and, for the non-selected frequencies, the impedance is less than said-internal resistance, and so determining the impedance of a frequency-dependent resistor in the plate circuit of the power stage of said amplifier that, for the non-selected frequencies, the 1m.-

pedance is substantially different from the internal resistance of the tube in said power stage.

4. The method of thermionic potential and power amplification in transmission systems, comprising amplifying, in an amplifier having a potential and a powerstage, all frequencies of the frequency band to be transmitted, selecting, in the potential stage of said amplifier, one of the two limit frequencies of said band for .more intense amplification than the non-selected frequencies, determining the impedance of a frequency-dependent resistor in the plate circuit of the potential stage of said amplifier so that, for the selected limit frequency, the impedance is of the order of, but not more than four times the internal resistance of the tube in the potential Stage of said amplifier, and, for the non-selected frequencies, the impedance is less than said internal resistance, and so determining the impedance of a frequency-dependent resistor in the Plate circuit of the power-stage of said amplifier that, for the selected frequency, the impedance is substantially equal to the internal resistance of the tube in said powerstage, andyfor the non-selected frequencies, the impedance is substantially different from the internal resistance of the last-mentioned tube.

5. The method of thermionic potential and power amplification in transmission systems, comprising amplifying, in an amplifier having a potential and a power stage, all frequencies of the frequency band to be transmitted, selecting, in the potential stage of said amplifier, one of the two limit frequencies of said band for more intense amplification than the non-selected frequencies, determining the impedance of a frequency-dependent resistor in the plate circuit of the potential stage of said amplifier so that, for the selected limit frequency, the impedance is of the order of, but notmore than, four times the internal resistance of the tube in the potential Stage of said amplifier, and, for the non-selected frequencies, the impedance is less than said internal resistance, and so determining the impedance of a frequency-dependent resistor in the plate circuit of the power-stage of said amplifier that, for the other limit frequency, the impedance is substantially equal to the internal resistance of the tube in saidpower stage, and, for the limit frequency which has been selected in the potential stage, as Well as for all intermediate frequencies of the band, the impedance is substantially different from the internal resistance of the last-mentioned tube.

6. The method of thermionic amplification in transmission systems, comprising amplifying, in a multistage potential and power amplifier, all frequencies of the frequency band to be transmitted, selecting certain limit frequencies, in certain potential stages of said amplifier, for more intense amplification than the non-selected frequencies, determining the impedances of frequency-dependent resistors in the plate circuits of the tubes of those potential stages of said amplifier in which a limit frequency has been selected, so that, for the selected limit frequencies, the impedances are of the order of, but not more than, four times the internal resistances of the tubes in the stages in which a limit fresaid internal resistances, and so determining the impedance of a frequency-dependent resistor in the plate circuit of the power stage of said amplifier that, for the non-selected frequencies, the impedance is substantially difierent from the internal resistance of the tube in said power stage.

7. The method of thermionic amplification in transmission systems, comprising amplifying, in a multistage potential and power amplifier, all frequencies of the frequency band to be transmitted, selecting certain limit frequencies, in certain potential stages of said amplifier, for more intense amplification than the non-selected frequencies, determining the impedances of frequency-dependent resistors in the plate circuits of the tubes of those potential stages of said amplifier in which a limit frequency has been selected, so that, for the selected limit frequencies, the impedances are of the order of, but not more than, four times the internal resistances of the tubes in the stages in which a limit frequency has been selected, and, for the non-selected frequen cies, the impedances are less than said internal resistances, and so determining theimpedance of a frequency-dependent resistor in the plate circuit of the power stage of said amplifier that, for the selected frequency, the impedance is substantially equal to the internal resistance of the tube in said power stage, 'and, for the non-selected frequencies, the impedance is substantially diiferent from the internal resistance of the last-mentioned tube.

8. The method of thermionic amplification in transmission systems, comprising amplifying, in a multistage potential and power amplifier, all frequencies of the frequency band to be transmitted, selecting certain limit frequencies, in certain potential stages of said amplifier, for more intense amplification than the non-selected frequencies, determining the impedances of frequency-dependent resistors in the plate circuits of the tubes of those potential stages of said amplifier in which a limit frequency has been selected, so that, for the selected limit frequencies, the impedances are of the order of, but not more than, four times the internal resistances of the tubes in the stages in which a limit frequency has been selected, and, for the non-selected frequencies, the impedances are less than said in ternal resistances, and so determining the impedance of a frequency-dependent resistor in the plate circuit of the power-stage of said amplifier that, for the other limit frequency, the impedance is substantially equal to the internal resistance of the tube in said power stage, and, for the limit frequency which has been selected in the potential stage, as well as for all intermediate frequencies of the band, the impedance is substantially different from the internal resistance of the last-mentioned tube.

ALBRECHT FORSTMANN. 

